The present invention relates to a method of operating printing apparatus, in particular inkjet printers, at least partly in a multi-pass mode, that is one in which a pen or printhead passes more than once over a horizontal band of the print medium. In each pass the printhead deposits a swath having only a fraction of the total ink required in each section of the image, with areas being left unprinted to be filled in during one or more other passes. A detailed account of how multi-pass printing may be achieved is discussed in U.S. Pat. No. 5,677,716.
One of the main limitations of thermal inkjet printing is the self-warming of the printheads due to the firing pulses (energy given to the printhead) needed to eject the ink. This warming can in many cases produce non-desired defects on print quality like thermal banding (big temperature excursions), puddling (printing at high temperature during a long time), or even damage the printhead itself (reaching very high temperatures).
Some of the solutions implemented in previous products set a minimum temperature of the printhead above ambient temperature (warming temperature) to avoid big temperature excursions, and then, depending on the type of object (text or graphics), use one printmode with more or less number of passes to avoid exceeding any unwanted temperature. Another solution is to set a maximum temperature and shut down (stop printing) or pause printing if the measured temperature is above a certain limit. A further solution is to change the carriage speed for different swaths.
To achieve multiple-pass printing, existing products define print modes that advance the print medium by a distance which corresponds to the printhead height divided by the number of passes to be undertaken. U.S. Pat. No. 5,677,716 discloses such an arrangement. In this arrangement, some regions are printed with reduced print medium advance and some regions with no medium advance; however these regions are restricted to the very top and bottom of sheets of print media to compensate for incomplete roller engagement.
EP-A-0863479 discloses a method for multipass printing in which, between each medium advance, a printhead scans in both directions printing, for example, two inks when scanning in a first direction and in two different inks when scanning in the opposite direction.
According to one aspect of the present invention there is provided a method of printing on a print medium with an inkjet printer in a plurality of horizontal swaths in which at least an intermediate region of the medium is printed in a multiple pass mode, characterised in that the passes are arranged in groups of p passes (where p is less than or equal to q, the total number of passes in the mode), no medium advance occurring between the members of each group.
The whole of the print medium may be printed in the multiple pass mode.
In a preferred method, p is equal to q and a full medium advance movement occurs between groups of passes. Such a method provides a good throughput.
In another preferred method, q is equal to rxc3x97p, where r is an integer greater than 1, and, between groups of passes, a medium advance movement occurs which is equal to a full medium advance movement divided by n. Such a method provides good print quality.
The integer p is preferably equal to 2. However, it may be greater than 2 if still higher print quality is required, or for other technical reasons.
In other preferred embodiments, the number of passes may be changed during the middle of a printing operation, i.e. xe2x80x9con the flyxe2x80x9d. The need for this can arise:
(i) when, due to dynamic temperature conditions, a prediction of the temperature of the printhead indicates an unacceptable value: and/or
(ii) when printing a file with mixed contents, e.g. graphics or high-density blocks plus text or thick lines, which have differing minimum levels of quality.
Of course, it is possible to print the entire file at the slowed speed/highest quality required, but this reduces throughput.
Some previously-proposed solutions also involve a substantial reduction in throughput since they involve more movements of the print medium and such movements are generally slower than movements of the printer carriage. Other previous solutions involve a high number of different passes and different medium advances, and these add complexity and higher memory needs to the firmware.
According to another aspect of the present invention there is provided a method of printing on a print medium with an inkjet printer in a plurality of horizontal swaths in which at least one first region of the medium is printed with a number n of passes, n being an integer, and at least one second region of the medium is printed with a larger number m of passes, m being an integer greater than 1, characterised in that in the or each second region a plurality of groups of passes occur with no medium advance occurring between the members of the groups.
The groups are preferably pairs of passes. When m is an even number, said plurality of pairs of passes occur in direct succession. When m is an odd number, the pairs of passes have extra passes interspersed between them. In preferred embodiments, the separation of successive pairs corresponds to a full print medium advance movement.
A uniform print medium advance movement is preferably maintained throughout the printing operation.
In one preferred embodiment n=1 and m=2 and the first region is printed using a first printing mask and the transition to the second region comprises the following steps:
printing of the last pass of the first region;
full medium advance;
printing with a second printing mask corresponding to half of an image to be printed;
printing with a third printing mask corresponding to the half of the image to be printed which is complementary to that of the second printing mask;
full medium advance.
The above process is substantially reversed for a transition from the second region to the first region.
In another preferred embodiment n=2 and m=4, and the first region is printed using a first printing mask and the transition to the second region comprises the following steps:
printing of the last pass of the first region;
half medium advance;
printing with a second printing mask having half the printing density of the first printing mask;
printing with a third printing mask having half the printing density of the first printing mask;
half medium advance.
The above process is substantially reversed for transition from the second region to the first region. Preferably the first printing mask comprises a top half (a), corresponding to half the image to be printed, and a bottom half (b), corresponding to the half of the image which is complementary to that of the top half, the second printing mask comprises first to fourth quarters (c, d, e, f) from top to bottom each corresponding to a quarter of the image to be printed, wherein the first and second quarters (c, d) if superimposed would be equivalent to the printing pattern of the top half (a), and the third and fourth quarters (e, f) if superimposed would be equivalent to the printing pattern of the bottom half (b), and the third printing mask comprises first to fourth quarters (g, h, i, j) from top to bottom and respectively corresponding to the second, first, fourth and third quarters of the second printing mask.
In a further preferred embodiment n=2 and m=3 and the first region is printed using a first printing mask and the transition to the second region comprises the following steps:
printing of the last pass of the first region;
half medium advance;
printing of intermediate pass with a second printing mask;
half medium advance;
printing with a third printing mask;
printing with a fourth printing mask;
half medium advance;
printing with a fifth printing mask;
half medium advance.
For a transition from the second region to the first region an intermediate pass is printed using a sixth printing mask. Preferably the first printing mask comprises a top half (a), corresponding to half the image to be printed, and a bottom half (b), corresponding to the half of the image which is complementary to that of the top half, the second printing mask comprises first to fourth quarters (k, l, m, n) from top to bottom, with the first and second quarters (k, l) together duplicating the top half (a), and wherein the third and fourth quarters (m, n) if superimposed would be equivalent to the printing pattern of the bottom half (b), the third printing mask comprises first to fourth quarters (o, p, q, r) from top to bottom with the first to third quarters (o, p, q) respectively corresponding to the printing pattern of the top half (a), the third quarter of the second printing mask and the printing pattern of the bottom half (b), the fourth printing mask comprises first to fourth quarters (s, t, u, v) from the top to bottom with the first, second and fourth quarters (s, t, v) respectively corresponding to the fourth quarter of the second printing mask, the printing pattern of the top half (a) and the printing pattern of the bottom half (b), wherein the fourth quarter (r) of the third mask and the third quarter (u) of the fourth mask if superimposed would be equivalent to the printing pattern of the top half (a), and the fifth printing mask comprises first to fourth quarters (w, x, y, z) from top to bottom and respectively corresponding to the fourth quarter (r) of the third mask, the third quarter (u) of the fourth mask, the third quarter (m) of the second mask and the fourth quarter (n) of the second mask. For the transition from the second region to the first region, the corresponding sixth printing mask comprises first to fourth quarters from top to bottom with the first quarter corresponding to the fourth quarter of the third mask, the second quarter corresponding to the third quarter of the fourth mask, and with the third and fourth quarters together duplicating the bottom half of the first printing mask.
According to a further aspect of the present invention there is provided a printer controlled to operate according to any of the above methods.